The specific aims of our Network proposal proceed from localizing g$ne$, to identifying candidate functional DNA sequence variation within these genes, to estimating the contribution of this DNA variation to the risk of EHYT. First, we will use linkage analysis to localize genes contributing to the risk of EHYT in three racial groups: African- Americans from Jackson, MS, Mexican-Americans from Starr County, TX, and Non-Hispanic Whites from Rochester, MN. The proposed linkage analyses will take advantage of the availability of both an extensive array of candidate genes and a large number of anonymous markers throughout the genome. We will use multiple diallelic sequence polymorphisms and cladistic analyses to begin to identify candidate functional sequence variation within a gene contributing to interindividual differences in BP levels and EHYT status. Finally, we will evaluate the ability of the candidate functional DNA sequence variation to predict EHYT status in three racial groups: African-Americans from Jackson, MS, Mexican- Americans from Starr County, TX, and Non-Hispanic Whites from Rochester, MN.